1. Field of the Invention
The invention concerns a casting mold for the production of muffles for use in dental prosthetic manufacture.
2. The Prior Art
Such a casting mold is known from "Das zahnrztiche and zahntechnische Vorgehen beim Teleskopsystem in der Prosthetik", "Dental and Dental Surgery Procedures using the Telescope System in Prosthetics" by Bottger and Grundler, Verlag Neuer Merkur GmbH, Munich, 1978. In order to be able to produce precise casting objects, such as crowns, bridges, inlays, onlays, telescopes and similar items from precious metals, the object must first be modeled in wax or a self-polymerizate. The wax model is subsequently provided with a casting channel, which serves for subsequent injection of the melt. The other end of the casting channel is attached to a funnel shaper in the form of a rubber socket. Subsequently, a pipe-shaped muffle ring is inserted into a depression located in the rubber socket with one part, and this ring then surrounds the wax model. Then the embedding mass is introduced into the casting muffle, with setting expansion occurring when the embedding mass sets, predominantly in the axial direction, since expansion of the embedding mass in a radial direction is prevented by the muffle ring.
After setting or curing of the embedding mass, the funnel shaper is pulled off from the set embedding mass and the muffle ring. The set embedding mass is subsequently heated to a temperature of 200.degree. C. with the muffle ring, in order to drive out the wax. After the wax has been driven off, the mold, i.e. the set embedding mass with the muffle ring, is placed in an oven and is heated until it has reached the temperature desired for subsequent casting, namely 700.degree. C. During this heating, thermal expansion takes place. Since the setting expansion mentioned above and the thermal expansion mentioned now predominantly occur in an axial direction, a distortion of the casting cavity in an axial direction takes place, which results in fitting inaccuracies of the casting object. To eliminate these fitting inaccuracies, other cost-intensive work procedures are then necessary.